Numerous compounds exist which are active pesticides useful in agriculture, or potentially useful in agriculture, which undergo relatively rapid degradation on exposure to sunlight. To be effective, an agricultural pesticide must be applied, generally by spraying or dusting, over a very wide area. When thus dispersed, light-degradable compounds rapidly lose their activity at a rate such that, in some instances, more than half of the initial pesticidal activity may be lost in as short a time as four hours after application.
Among the commonly used agricultural pesticides which are subject to serious degradation are insecticides such as pyrethrin, allethrin, and microbial insecticides such as the endotoxin of Bacillus thuringiensis. Among the potentially useful pesticides which would perhaps find widespread acceptance, if commercially available in a stable formulation, are the viral pesticides exemplified by the nuclear polyhedrosis virus of Heliothis, which are useful against the troublesome cotton bollworm. Exemplary of light-degradable herbicides is 4-hydroxy, 3,5-diiodobenzonitrile (Ioxynil).
It has been heretofore proposed to stabilize chemical insecticides against sunlight-induced degradation by the incorporation of ultraviolet absorbers. In U.S. Pat. No. 2,011,428, it is proposed to protect pyrethrin-based insecticides by incorporating in the formulation a substituted amino anthraquinone. Similarly, U.S. Pat. No. 2,772,198 proposes the incorporation of p-amino azobenzene. U.S. Pat. No. 3,113,066 proposes the incorporation of unspecified light absorbers in Bacillus thuringiensis-type microbial insecticides.
It is an object of this invention to provide an effective pesticidal composition including an effective amount of a sunlight-degradable pesticide and a stabilizing material in an amount sufficient to substantially retard degradation of the active pesticidal principle upon exposure to sunlight under typical conditions of application.
It is a further object of the invention to provide such a composition in which the stabilizing compound is not only effective, but also compatible with microbial and viral insecticide materials which contain viable spores or virus particles which may be destroyed by many conventional chemical additives.
As used in this specification, the term "pesticide" or "pesticidal composition" refers to compositions which are useful in agriculture to control agricultural pests, especially detrimental insects, but also including non-insect pests such as mites, fungi, and noxious or detrimental weeds. Thus, the pesticidal composition may be, for example, an insecticide, a herbicide, a fungicide, or miticide.
Briefly, the pesticidal compositions of this invention comprise an agronomically acceptable carrier having dispersed therein a light-degradable pesticide in an amount sufficient to control a target pest, and a stabilizer for the pesticide in an amount effective to substantially retard pesticide degradation upon exposure to sunlight under typical conditions of agricultural application. The stabilizer is a sulfonated copolymer of catechin and leucocyanidin having a molecular weight in the range of about 3,000 to 6,000. Especially preferred are non-phytotoxic metal and ammonium salts of such sulfonated copolymers, especially magnesium, zinc, manganese, and alkali metal salts.
The active pesticidal ingredient of the composition is any agricultural pesticide which is subject to rapid degradation upon exposure to sunlight. By this we mean a material which is degraded at a rate such that its effectiveness as an agricultural pesticide is substantially impaired or reduced. The active material may be effective against any agricultural pests such as weeds, insects, mites, fungus, or the like, or against a combination of such pests. The active pesticidal material will be dispersed, in accordance with conventional and well-known practice, in a suitable carrier. Such carriers may be a dry powder such as clay or talc, or may be an organic-based liquid adapted for spray application or for admixture with water to form an aqueous emulsion. Water itself is perhaps the most widely used carrier for pesticidal compositions. It is readily adapted for use in the formulation of compositions which will be further diluted just prior to application by addition of water. The active pesticidal ingredient may itself be soluble in water or may be solubilized or dispersed by the incorporation of a surface active agent, all as is well known and understood in the art.
The stabilizing ingredient in accordance with this invention is a polymer derived from 15 carbon atom monomers that are flavenoid in structure. The two basic flavenoid structures are: ##STR1##
The polymeric form in composed essentially of the two above-mentioned monomers is about a 1:1 ratio.
As the structures illustrate, the polymer has high content of phenolic hydroxyl groups thus ensuring high polarity and considerable water solubility. This solubility is enhanced by the presence of the sulfonate group.
Polymers having a molecular weight of about 3,000 to about 6,000 are especially preferred. The effectiveness of the stabilizing agents is enhanced when the sulfonate group is neutralized to form a metal salt. The metal may be any one which is non-phytotoxic, but preferably will be selected to enhance the water solubility of the polymer. Exemplary are the ammonium, zinc, manganese, magnesium, and alkali metal salts. Especially preferred is the sodium salt.
The sulfonic acid content expressed as SO.sub.2 in the resulting polymer therefore constitutes about 9.5 to 12 weight percent of the total polymer weight, more usually about 11.5 weight percent.
The sulfonated copolymers and the unsulfonated copolymers from which the sulfonated copolymers are derived are known materials and may be produced in accordance with established procedures. The unsulfonated copolymers are traditionally obtained from a natural source, i.e., by the treatment of hemlock bark by known procedures. The unsulfonated copolymer thus obtained is then sulfonated under controlled conditions in a conventional manner to introduce approximately one sulfonic group. The resulting sulfonated copolymer may be then treated with the appropriate inorganic base, e.g., sodium hydroxide, to obtain the salt form which may be desired. It is generally preferred that the reaction with the organic base be effected and more preferably that it be conducted so that the sulfonated salt will be substantially neutral in aqueous solution, i.e., provide a pH in the range of about 5.5 to 7.5, more preferably a pH of about 7.
The sulfonated copolymers are incorporated in the insecticidal composition in an amount to provide about 1/4 to 2 lbs. of the sulfonated copolymer per acre treated, and more preferably about 1/2 to 11/2 lbs. per acre. It will be understood that, within very wide limits, the actual concentration of the active pesticidal ingredient and the sulfonated copolymer in the pesticidal composition is not important. More or less dilute compositions may be effectively used, and sometimes preferred, in certain agricultural applications. The active pesticidal ingredient and sulfonated copolymer are applied on a per acre basis by the expedient of employing larger quantities of the more dilute material or lesser quantities of less dilute material.Thus, for aerial application, low dilutions are generally employed while greater dilution may be desired for use in conventional ground-spraying rigs to minimize problems of uneven distribution due to sprayer-clogging and the like. Nevertheless, a definite relationship between the amount of the active pesticidal composition and the sulfonated copolymer will be maintained. For example, an aqueous base formulation may be intended to provide 1/2 lb. per acre of pyrethrin, and in accordance with this invention, 1 lb. per acre of sulfonated copolymer. Thus, the ratio of pyrethrin to sulfonated copolymer in the formulation will be 0.5 to 1.0, while the percent of pyrethrin in the composition may vary within the ranges of, say, 1 to 10%, based on the weight of the total composition.
A number of experiments have been performed which demonstrate the efficacy of the sulfonated copolymers of this invention in retarding the degradation of sunlight-degradable pesticides. In the experiments of the following examples exposure to sunlight means exposure to natural sunlight under typical field conditions. Exposure to artificial light means exposure, for the period specified, to artificial sunlight produced by a bank of ten General Electric F-30-T8-BL lamps set three inches apart. Samples were exposed at a distance four inches from the axis of the center lamp. Short wave ultraviolet light at the sample plane was measured at 1.4 mW/cm.sup.2. Long wave ultraviolet light at the sample plane was measured at 2.0 mW/cm.sup.2.
Sample formulations containing the pesticide, with or without the addition of a sulfonated copolymer in accordance with this invention, were applied to a glass plate. The amounts of light-degradable pesticide and protecting copolymer applied to the plate, on an area basis, are expressed in terms of weight per area, usually grams per acre.
The sulfonated copolymer employed in accordance with this invention, in the following Examples, unless otherwise specified, is the sodium salt of sulfonated copolymers of catechin and leucocyanidin having an average molecular weight in the range of about 3,000 to 6,000, the sulfonated copolymer being neutralized to a pH of approximately 6 and being obtainable commercially from ITT Rayonier Inc. under the designation HT-193.